Agreed.
But I think it will be hard to collect the new funds in time (do not expect everybody to read/be noticed, to agree or just to transfer money (especially those from foreign countries where fees would exceed the requested amount).
Furthermore I would like you to put a statement that those parts are belonging to the donators (in contrary to R&D donations). In case of bankrupcy (beware) I do not want to deal with an 'Insovenzverwalter'. And take a look into future what resources might have the same prob, so if that happens request full amount of desired money, not slice by slice.

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positive aspect:
this will give you another chance to correct estimation of real number for to-be-expected orders.